The Susan and Diana Au oxide mineralization of Corihuarmi are associated with epithermal deposit types. Epithermal gold deposits form in hydrothermal systems related to volcanic activity. These systems, while active, discharge to the surface as hot springs or fumaroles.

Epithermal gold deposits occur largely in volcano-plutonic arcs (island arcs as well as continental arcs) associated with subduction zones, with ages similar to those of volcanism. The deposits form at shallow depth, <1km, and are hosted mainly by volcanic rocks.

There are two end-member styles of epithermal gold deposits, high sulfidation (HS) and low sulfidation (LS). The two deposit styles form from fluids of distinctly different chemical composition in contrasting volcanic environment. The Diana and Susan deposits are of the HS style.

Mineralization identified to date within the Corihuarmi Project comprises a high sulphidation epithermal precious metal system that formed at relatively shallow depth. Gold and silver mineralization is essentially confined to remnant zones of silicification and brecciation that dominantly lie along the northeast margin of the volcanic complex. Horizontal metallogenic zonation provides evidence that this siliceous layer was once continuous, effectively capping the hydrothermal system.

The most significant mineralization is associated with the Susan and Diana zones, which comprise resistant remnant mineralized silicified bluffs separated by some 180m. The Susan deposit measures approximately 200m by 350m in size, being confined at the margins by cliffs. The smaller Diana Zone is approximately 150m by 250m in area, and to some extent remains open to the northwest and southeast along the ridge-line. The siliceous layer is shallow dipping to sub-horizontally disposed, ranging in thickness from 10m to 75m, and averaging approximately 45m.

Gold mineralisation is mined by open pit methods at a mine production rate of 9,000 tonnes per day (t/d) of ore and 5,000 t/d of waste. The average grade produced in the last year (2017) is around 0.27 g/t and it is expected 0.28 g/t will be produced in the following years (2018 to 2020).

Mining at Corihuarmi uses a conventional truck and excavator configuration. Open pits are mined on 5-meter high benches through drilling, blasting, loading and hauling unit operations. The material transportation circuit is performed in two parts, the first one is from the pit to the crusher and the second one from the crusher to the leach pad. If the ore does not require additional crushing, the material is transported directly to the leach pad.

The waste is transported to the waste dump. The mine schedule was produced in monthly periods and is based on 7 small pits which will be mined throughout 3 years of mining operations.

Crushing
Ore from the mine, with a moisture content of 4 to 5% is transported by trucks to the Run of Mine (ROM) pad. The ore is then either dumped directly into the coarse ore bin (COB) or can be placed on the ROM pad and fed into the COB by front end loader.

Ore is withdrawn from the COB by a vibrating scalping grizzly feeder with 100mm gap size. The plus 100mm is fed into the primary jaw crusher. The minus 100 mm grizzly undersize material and the crusher product both drop onto the jaw crusher discharge conveyor. As the ore travels along the conveyor it is weighed, and lime is added. From this conveyor the ore is discharged onto a stacking conveyor and is stockpiled. The crushed material is reclaimed using a front-end loader and trucks and transported to the heap leach pad.

The Project is a heap leach operation utilizing a multiple-lift, single-use leach pad. Prior to placing the ore onto the leach pad the ore is primary crushed. Processing of ore began in January 2008 when irrigation of the heaps was started.

Heap Leaching
Heap Leaching is carried out in a single stage system. Pregnant Leach Solution (PLS) is delivered to activated carbon contactors to remove the gold after which the solution is pumped back to the heap leach pad. The activated carbon in the contactors is stripped from the carbon in a Zadra elution plant and the gold is electrowon onto cathodes. Sludge is removed from the cathodes and retorted to recover mercury prior to being direct smelted to recover the gold into bullion ready for sale.

The current heap leach pad covers an area of nine hectares and is designed to treat 6000tpd. Trucks enter the leach pad via a ramp at one end and dump the ore within one to two metres from the edge of the heap. A bulldozer i ........